(1) Field of the Invention
The invention relates to a method for repairing cracks in metal parts using cathodic arc coating and Hot Isostatic Pressing processes.
(2) Description of the Related Art
It is common for gas turbine engine components to develop, over the course of their operation, cracks that originate on the surface of the component and extend into the component or vice versa. Such cracks primarily arise over time from the extreme temperatures and pressures experienced by the turbine engine components. Of particular concern are cracks which form in turbine components comprised of superalloy materials such as nickel-based superalloys. Such materials tend to produce equiaxed, directionally solidified, and single crystal alloy structures.
Unfortunately, presently utilized methods for repairing such cracks suffer from significant drawbacks. Examples of such presently employed methods include Activated Diffusion Healing (ADH) or Turbofix™ diffusion brazing, welding, and the use of High Velocity Oxy-Fuel (HVOF) spray materials. ADH/Turbofix diffusion brazing typically employs a mixture of braze and base alloy to seal the crack. Properties of the braze and base alloy typically exhibit less than 50% of the strength of the base material on equiaxed alloys. When applied to directionally solidified and single grain alloys, the braze and base alloy repair material exhibits strength properties which are significantly lower than 50% of base material. Attempts to weld base material into cracks suffer from different drawbacks. Specifically, it is difficult to apply through a process of welding a material onto a superalloy component without inducing further cracking, typically due to the localized heat input from the welding operation. In addition, in instances where the weld is successful, the properties exhibited by directionally solidified and single crystal alloys exhibit significantly lower strength than the original part. Lastly, the application of HVOF spray materials similarly suffers drawbacks. Specifically, because the process seals the cracks in an air atmosphere, the ability to seal and bond the crack is inhibited as a result of the presence of oxidation. Moreover, HVOF processes induce oxidation in both the material being applied, and the part to which the material is being applied. The internal oxidation of the part and the oxygen content of the applied alloy lessens the resulting strength of the repair.
What is therefore needed is a method for repairing cracks in metallic parts, particularly gas turbine engine components, which can seal and repair the crack with an alloy resulting in a repair exhibiting material properties which approach that of the base material from which the part is constructed, and which is usable on an equiaxed, directionally solidified and single crystal alloys.